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The chemical analysis of muscle biopsies from patients with Duchenne muscular dystrophy has revealed several abnormalities of calcium regulation. The calcium content of the muscle cells is elevated and the sarcoplasmic reticulum is less able to regulate the calcium within the cell. Furthermore, two calcium-binding proteins, including calsequestrin, were found to be abnormally low in Duchenne dystrophic muscle cells. To further investigate the abnormalities of calcium regulation in these cells, investigators have examined both the calcium-sensitive protein calmodulin and the calmodulin-dependent enzyme, calcium-ATPase. It was found that calmodulin is elevated in the muscle cells of Duchenne dystrophy patients, and the elevation is greater in early stages of the disease and in patients whose disease is progressing more slowly. Indeed, the calmodulin content in cases of advanced disease is within the normal range. Calcium-ATPase activity was reduced in the Duchenne muscle cells; the addition of more calmodulin in the laboratory did not succeed in raising the activity of this enzyme. The results indicate that abnormalities in calcium regulation are among the first changes to occur in the progression of Duchenne muscular dystrophy. The authors suggest that these abnormalities are involved in the progression of the disease. (Consumer Summary produced by Reliance Medical Information, Inc.)